The Fresh Loaf

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Hydration: Effect of potatoes?

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Scott Grocer's picture
Scott Grocer

Hydration: Effect of potatoes?

Does anybody have a good rule of thumb for calculating the hydration of a dough when it includes plain, cooked and mashed potato?

According to the USDA: Potatoes, baked, flesh, without salt (100 grams) contain on average 75.42 grams of water. That sounds right I guess, but how much of that moisture is available to the dough, and how should I adjust hydration in relation to potato content?

Thanks

cranbo's picture
cranbo

so 75% of baked potato is water? wow. 


I asked a similar question about potato substitution awhile back but never got a definitive answer, except "try it and see".


I guess try it out: assume that a baked potato has between 50-75% of water (giving a minimum to maximum range), so then per 100g of potato, assume 50-75g of water is available to your dough.


Let us know how it turns out!

possum-liz's picture
possum-liz

From my experience, normal mashed potato can be added to the dough without adjusting dough hydration. My doughs usually run about 67-70% hydration and I add about 100 grams potato to a medium loaf. If you're not using 'leftover mash' you need to up the salt a little.

subfuscpersona's picture
subfuscpersona

What is the baker's percentage for the "100 grams potato" that you add to your dough?


If you don't know, can you at least give the total flour weight (in grams) of the formula you use when you add the 100 grams of mashed potato?


Thanks

cranbo's picture
cranbo

not exactly possum-liz's answer, but I've used 60g of baked potato very successfully in a dinner roll recipe. Bakers % was 16.67% (total flour was 360g). I didn't have to adjust the hydration much, if at all, as I recall. 


I imagine if you start getting into 25% range, you might have to pay more attention to the hydration. 

possum-liz's picture
possum-liz

The baker's % of mashed potato runs at about 16 -20%, sometimes it varies a bit depending on the leftovers. Much higher and the bread seems to be a bit gummy.


Liz

AnnaInMD's picture
AnnaInMD

and used almost raw - partially microwaved potatoes and a second batch with salt water boiled potatoes. The crumb from the almost raw ones was much moister, so I will adjust my water to a bit less the next time.  The crumb from the other batch came out perfectly without adjusting for water. Since most recipes call for fully cooked potatoes, their water content has already been reduced quite a bit.


anna

emmsf's picture
emmsf

I recently asked a question about the effect on hydration of soakers, and I think the answer there will be instructive here.  I am told that the Bread Bakers Guild of America recommends that soakers should be "hydration neutral" and though there's some debate on what that means, the general sense is that soakers should neither add to, nor take from, the water available to the flour.  How you achieve this is up for debate, but  the concept seems simple enough.  Just as with soakers, the goal with potatoes should be hydration neutrality.  If the potatoes are wet, you should drain them and include the potato water when measuring the overall water for the formula.  Or if you want that extra moisture, drain them, measure the potato water, add it to the formula, and raise the hydration % accordingly.  If you are unable to drain the potatoes in any meaningful way, even by pressing in a seive or squeezing in a cloth, I'd leave the hydration % alone and rely on a bit of trial and error.

Scott Grocer's picture
Scott Grocer

I wrote to a professional baker for clarification re: this subject and he was kind enough to respond.

Q: "Is there any reasonable way to calculate the hydration of a dough that includes plain, unadulterated, cooked and mashed potatoes?"

A: "There sure is, just figure the potatoes at 90% water content, then use this as part of the total dough absorption. This is the same thing you would do if you were adding liquid eggs to the formula and calculating the total dough absorption."

Note: In my email I did not clarify whether the potatoes had been boiled, skin on or off, or had extra liquid added to facilitate mashing. I suspect that could have lead to the water percentage in his reply being higher than I'd expected.

I also suspect it could be safer to assume the potato had a slightly higher hydration than the USDA numbers, as it's always easier to add moisture during mixing than to remove it.

I hope to experiment as time permits and report back.

Thanks!

emmsf's picture
emmsf

I must admit I'm confused.  The pro compares potatoes to liquid eggs.  But whereas liquid eggs provide water which is immediately available for absorbtion by the flour (the very definition of "hydration"), the same is not true of cooked potatoes.  A potato may be 90% water, but it certainly does not contribute 90% of it's weight as water available for absorbtion by the flour.  Most, if not all, of the water is already bound by the starches in the potato.  The percentage of water in an ingredient is irrelevant to the calculation of "hydration" unless that water can be absorbed by the flour. 

Scott Grocer's picture
Scott Grocer

I think I'll fire off an email to a few food scientists whose email addresses I found, maybe I'll get lucky.

Scott Grocer's picture
Scott Grocer

On a long shot I sent emails to a USDA food scientist, a certified master baker/culinary instructor working for a university and the King Arthur Flour baking hotline for good measure. And they wrote back!

The USDA Scientist: "Here is my guess: 100grams of potatoes have 75 grams water and 25 grams dry matter, about 70% of the dry matter is starch. So the amount of dry starch/100grams fresh potatoes = 100x 0.25 x 0.70 = 17.5 grams.

Water absorption of potato starch: 0.54 g water/g dry starch (Evans et al. 1982, Effect of solutes on gelatinization temperature range of potato starch, Starch, vol. 34, S. 224-231).

The water absorbed by starch in potatoes would be = 17.5 grams starch x 0.54 = 9.5 grams water. Assume that other 30% dry matters (pectins, cellulose etc.) may absorb about 2-3 grams of water, that leads to a total of 12.5 grams.

Therefore, a rough estimate for the amount of available water = 75- 12.5 = 62.5 grams/100grams of potatoes."

The CMB/culinary instructor: "Because the potatoes have been roasted, there is no unbound water to account for. Hydration does not decrease."
King Arthur Baking Hotline: "I'm sorry, we do not have this information. Since the starch in potato is very weak, I would expect almost all of the moisture to be available. Give it a try."
emmsf's picture
emmsf

Fascinating.  Thanks for posting these replies. 

Mini Oven's picture
Mini Oven

If you are interested, there is a dumpling known as a mehlknödel (flour dumpling) from the area north of Linz.  It does not rise while there is no leaven but the recipe calls for equal weight of cooked potatoes to AP flour, salt to taste.  The cooked potatoes are put thru a ricer and flour is added and tossed to make flour coated crumbs.  I usually get more flour in than the recipe as potatoes do vary and mine seem to send out a lot of moisture, especially if the potatoes are still warm and steaming. (so if you go about comparing recipes there is a difference when using cold standing potatoes to just cooked warm ones, the cold potato recipes tend to give off less water and therefore flour amounts tend to be lower.)


I add enough flour until the crumbs just hold together into a ball.  If not enough flour is added, the dumplings will be solid and not absorb any roast meat juices.  They are boiled in salted water for about 20 minutes or until the flour inside no longer powders.  The outside 2mm will be gelled and the rest of the crumb should be flecked with flour and potato.  They are heavy but extreme Soaker-uppers.  I should add that a lot of gluten development is not desired.


So where does this info come in?  


I just wanted to mention the extreme hydration scenario in use.  Steam coming off the potatoes is a hydration factor used both before and during baking/cooking (and if you need to stretch 3 - 4 medium potatoes to feed a crowd, you can do it with about a 3/4 kg of flour, but have plenty of juices or very thin gravy.)  Cold leftover day old dumplings can be sliced and are very similar to vollkorn bread in texture eaten with cold cuts, onion/pickle and something wet like left over gelatinized roast juices, garlic mayo, mustard or horseradish creme.  I wouldn't pan fry them cut up for they just might break into a pile of crumbs.